RAMAN AND INFRARED-SPECTRA OF HYDROUS BETA-MG2SIO4

Micro-Raman and micro-infrared spectra of the silicate and OH-stretchi ng regions have been obtained from a well-characterized crystal of hyd rous beta-Mg2SiO4 containing approximately 2.6 wt.% H2O. Five distinct OH-stretching vibrations were observed in two separate spectral group ings. A Raman-active band at 3355 cm(-1) and an infrared band at 3351 cm(-1) comprise the first group; a Raman band at 3583 cm(-1) and infra red bands at 3596 and 3653 cm(-1) make up the second group. These resu lts are consistent with the incorporation of H into the O1 site. The a pparent division of the OH-stretching bands into a group near 3330 cm( -1) and a group near 3600 cm(-1) is due to differences in the lengths of the hydrogen bonds to the nearest-neighbor oxygen atoms in the Mg2 and Mg3 octahedra. Relative intensities of the bands suggest that a ma jority of shorter, and hence, stronger hydrogen bonds are formed in th e hydrated beta phase. Tentative assignments of the observed bands hav e been made by comparison with the corresponding spectra of anhydrous beta-Mg2SiO4.